1. Field of the Invention
The present invention relates in general to a heat seal blister package for housing a product and, more particularly, to a heat seal blister package having improved moisture vapor transmission properties to house a product which is moisture sensitive.
2. Background Art
Blister cards and blister packages have been known in the art for many years. Typically, a clear plastic blister made of PVC or other similar material is adhered to a paperboard card or backing panel to form an enclosed pocket to house a product therein. The plastic blister provides an airtight seal to protect the product, while allowing a potential consumer to view the product through the clear plastic blister. The paperboard card or backing panel typically provides an opportunity for labeling, identifying or advertising the product.
It has been a common practice in the art to attach the plastic blister to the backing card via a heat seal. In particular, heat seal coatings, such as polyurethane-based coatings, are typically used to coat one side of the backing card. The heat seal polyurethane coatings are typically applied to the backing card in an off-set printing process. Upon coating the backing card, the plastic blister is then applied to the card with heat to bond the plastic blister to the underlying backing card.
Although these and other prior art heat seal blister packages employing a heat activated sealing coat, including those polyurethane-based heat seal coats, have worked well for the packaging of a wide variety of articles, conventional heat seal coatings can often provide little or no barrier to prevent or impede the transmission of moisture vapor from the surrounding environment through the paperboard backing card and into the enclosed pocket where the product is typically housed. While the plastic blister usually forms an impermeable barrier to moisture transmission, moisture from the surrounding environment can often penetrate through the paperboard backing card.
Thus, although moisture vapor transmission barrier properties may be unimportant for the housing of certain products in blister packages, such as inedible ones, or products not affected by exposure to humidity, etc., other products are moisture sensitive. For instance, moisture vapor penetration into the blister package may be particularly troublesome in the context of edible products, which can be highly moisture sensitive. For these and other types of moisture-sensitive products, the penetration of moisture vapor through the paperboard backing card can lead to degradation or destruction of the product contained within the blister package.
Moreover, coatings which possess moisture vapor transmission barrier properties are also known. In particular, these coatings have been employed in paperboard products to prevent moisture infiltration into various moisture sensitive products. For example, coatings having moisture vapor barrier properties have been used to coat detergent boxes, as moisture vapor penetration into powder detergent has been known to cause clumping or other degradation of the detergent. However, these moisture vapor transmission barrier coatings are not known to have been used in a context of heat sealing plastic to paperboard—particularly in the environment of forming a blister package.
Accordingly, it is desirable to provide a blister package in which the coating applied to the paperboard card or backing panel possesses not only the capability of forming a heat seal bond with a plastic blister, but also the moisture vapor transmission barrier properties to hinder penetration of moisture vapor through the backing card and into the interior of the blister package.
It is likewise desirable to provide a process for forming a heat seal blister package having improved moisture vapor transmission barrier properties. As part of this process, it is desirable to employ a rotogravure process for application of the heat seal coating, to closely control the weight range of the coating as applied to the paperboard backing card.